Choosing private IPv4 address range for internal network

If you are in IT consulting field many times you will be assigned task of creating IPv4 addressing for enterprise. Here we will pass on to you our experience of designing internal IP addressing using private IP range.

On internal network we will use private IP range which is defined in RFC 1918.

Private IP Addresses characteristic

Delay the transition to IPv6

Require NAT translation

Can not be routed to the Internet

Number of networks must be reserved in each Address Class

Dedicated for use on the Internal networks

IP Addresses reserved for use on private networks

Address Class

Reserved Address Space

Class A

10.0.0.0 to 10.255.255.255

Class B

172.16.0.0 to 172.31.255.255

Class C

192.168.0.0 to 192.168.255.255

Choosing internal IP range

When we are taking on a task of designing internal IP range in most cases we would suggest using Class A for any size internal network. The reason for this is simple. Class A gives us the most flexibility and room for expansion and growth. In some cases when you setting up very small office and you know there will be no more then few devices then class C should be fine.

Quick example

We are designing Internal network with 10 internal departments separated by internal Vlans. We will in this case use class A with /24 mask

10.10.1.0/24, 10.10.2.0/24, 10.10.3.0/24 ……

This will give us 256 hosts per network and plenty of room for growth.